Current techniques in electron microscopy will be used to study the ultrastructural features of several pathogenic rickettsiae in various host cells. Rickettsia mooseri and Rickettsia prowazeki will be examined in the flea and body louse tissue. In addition Rickettsia conori, Rickettsia tsutsugamushi, Rickettsia rickettsi and Rickettsia quintana will be studied in various cell cultures. Along with transmission electron microscopy, scanning and high voltage electron microscopy will be used. Labeled antibodies to various rickettsiae will be used to demonstrate surface antigens at the ultrastructural level.